The paper being a bad conductor of heat, prevents the lead from solidifying immediately it leaves the ladle, and as by long practice the workman always ladles out the same quantity of lead, the sheets made vary but little either in site or thickness.
Leaden pipe is made by forcing the partially congealed molten lead through dies, In which a core is inserted, by hydraulic pressure. The essential part of the apparatus for this purpose is eihibited in section in Fig. 145.
The die a ia simply a metallic disc, in which is an aperture which fixes the outside diameter of the pipe to be made. This opening flares downward. The die is inserted in a collar which, in turn, rests in the bed - piece, and ia adjustable so as to bring the die accurately in line by means of the set - screws b. Resting above die and bed - piece is the lend receptacle c. This is a heavy cylinder having an annular chamber formed in it to receive the steam by which it is kept hot. d is the press - plunger working downward, and in it is inserted the core e, which enters the die aperture. The metal is drawn off directly from the kettle, and the plunger is at once brought down upon it, so that it may be kept under moderate pressure until sufficiently congealed. The press is then set in operation, and the lead is forced through the annular space between the core and die, and emerges in the form of pipe. The process is quite rapid, and there is nothing further to do but reel - up the pipe as it is drawn. As soon as one charge is exhausted, or rather partially so, as a portion in left in the chamber, to which the new charge unites, more lead it admitted from the furnace, and the operation is repeated. The amount of pipe made at a single pressure depends upon the weight of same when finished.
Thus an extra - light 1 - in. pipe weighs 2 lb. to the ft., and the chamber may, for example, hold 135 lb. Therefore 67 1/2 ft. of pipe are produced at each descent of the plunger. Different sizes of pipe are produced by substituting suitable dies and cores. The die is easily reached by lifting the chamber e, which is done by attaching the same to the press - plunger and elevating the latter.
Tin - lined leaden pipe is produced somewhat differently. Before the lead is run into the chamber, a mandrel is inserted, which closes the die aperture and extends up through the receptacle. This mandrel consists of a central stem, around which are grouped dovetailed sections, so that when the central portion is removed the sections are easily taken out, leaving a hollow space in the lead which is run in while the mandrel is in place. The sides of the mandrel are tapered, or rather crenelated, there being 3 or 4 shoulders and a different taper from each. The object of this is that after the mandrel is removed, the tin which is poured into its place may have several purchases against the lead which surrounds it. Of course before the tin is let in, the core, as already described, is inserted. Afterwards the pressure is applied in the usual manner, the result being that the pipe emerges with a thin lining of tin. Tin - lined leaden pipe and plain leaden pipe weigh the same.
Shot, though sometimes made of lead alone, is almost always formed of an alloy of arsenic and lead, the arsenic being introduced in the form of arsenious acid or the sulphide (orpi - ment). The object of the addition of the arsenic is to slightly harden the lead, and render it capable of cooling to a globular form. Owing to the rapid decomposition of the arsenic, it is treated by itself in the bottom of the melting - kettle shown in Fig. 146. A cover is placed over the substance, and its stem, which rises up through the kettle, is fastened down. The lead is then added above the cover, and, when melted, the cover is lifted out of the liquid mass, which instantly becomes permeated by the arsenic beneath. The alloy thus produced contains 45 lb. of arsenic to the ton of lead, and is known as "temper." This again is added in the proportion of 1 Per cent. to the pure lead, and thus the shot alloy, containing a very small percentage of arsenic, is produced. The making of quantities of the temper at a time is a great convenience, as the proportion of arsenic in the shot is thus kept uniform, while the melting can be done in the ordinary kettle in the sum - rait of the shot - tower.
The temper - pots hold about a ton of metal each, and the cooled product has a brownish gloss distinguishing it in a marked manner from the dull hue of the pure lead.
The manufacture of shot is almost universally conducted in tall brick towers with iron frames. In the top chamber is a melting - pot, whence the molten lead is dipped by workmen wearing thick gloves and wielding iron ladles. The metal is poured into colanders, which are simply perforated copper pans, resting in iron rings fastened over the well of the tower. In the bottom of the colander is placed a layer of the dross which rises to the surface of the lead during melting. This in a measure checks the too rapid escape of the melted metal, and is thought to have the effect of increasing the rotundity of the shot, possibly by expediting its cooling as it passes through. The holes in the colanders vary from 1/30 to 1/360 in., but the shot are of larger diameter than the orifices. In falling to the base of the tower, the particles of semi - fluid lead, acted upon alike over their whole surface by a current of air, are made to assume the globular form, and by the time they reach the bottom they are sufficiently hardened by cooling to bear the shock of striking the surface of the water in the well below. The size of the shot is only approximately fixed by the sizes of the holes in the colanders.
The mass is always larger than the hole from which it exudes, and as the period of dropping is not exactly uniform, perhaps half - a - dozen sizes are produced from the same sieve. Again, large - sized shot require to be dropped from a greater height than small - sized, and while in some cases 100 ft. is sufficient, in others an elevation of 150 ft. is hardly enough. Buckshot, as will be explained further on, are not made by the dropping process at all, owing to their size.